Introduction. Low dose technology of an EOS scanner allows mechanical axis radiographs to be produced using a continuously moving x-ray emitting a thin beam to form a single image which includes all three joints, without the need for stitching. The aim of this study was to identify necessary improvements to enable effective interpretation of the radiographs, and to assess whether the quality of the radiographs varied by production method compared to a previous audit of CR and DR radiographs. Materials and Methods. 8 domains were identified based on a previous audit using the acronym MECHANIC each defining the qualities required for a radiograph to meet the criteria. 100 mechanical axis radiographs produced using conventional and digital methods were analysed in the original study to assess how many radiographs met the described criteria. The same criteria were amended and used to assess 123 different mechanical axis radiographs in the follow up study following the introduction of the EOS scanner, in which 77 were produced using EOS and 46 were produced using conventional and digital methods. Results. The second study showed improvement in 2 of the 6 domains being assessed and the result remained the same in 1 domain, with a mean change of +2%. There was a large increase in the number of radiographs with impeccable stitching in the second study due to the use of the EOS scanner. When comparing the methods of production, there were a greater percentage of EOS radiographs meeting the criteria for each domain compared to conventional and digital radiographs. Those produced using the EOS scanner had a mean 0.83% more radiographs meeting the criteria per domain. Conclusions. The overall quality of mechanical axis radiographs being produced has increased, but varies largely between the 6 domains. The EOS produced radiographs overall were of a greater quality than those produced using conventional and digital methods, but still had areas which required significant improvement

The emergence of patient specific instrumentation has seen an expansion from simple radiographs to plan total knee arthroplasty (TKA) with modern systems using computed tomography (CT) or magnetic resonance imaging scans. Concerns have emerged regarding accuracy of these non-weight bearing modalities to assess true mechanical axis. The aim of our study was to compare coronal alignment on full length standing AP imaging generated by the EOS acquisition system with the CT coronal scout image. Eligible patients underwent unilateral or bilateral primary TKA for osteoarthritis under the care of investigating surgeon between 2017 and 2022, with both EOS X-Ray Imaging Acquisition System and CT scans performed preoperatively. Coronal mechanical alignment was measured on the supine coronal scout CT scan and the standing HKA EOS. Pre-operative lower limb coronal alignment was assessed on 96 knees prior to TKA on the supine coronal scout CT scan and the standing HKA EOS. There were 56 males (56%), and 44 right knees (44%). The mean age was 68 years (range 53-90). The mean coronal alignment was 4.7 degrees (SD 5.3) on CT scan and 4.6 degrees (SD 6.2) on EOS (p=0.70). There was a strong positive correlation of coronal alignment on CT scan and EOS (pearson. 0.927, p=0.001). The mean difference between EOS and CT scan was 0.9 degrees (SD 2.4). Less than 3 degrees variation between measures was observed in 87% of knees. On linear regression for every 1° varus increase in CT HKA alignment, the EOS HKA alignment increased by 0.93° in varus orientation. The model explained 86% of the variability. CT demonstrates excellent reliability for assessing coronal lower limb alignment compared to EOS in osteoarthritic knees. This supports the routine use of CT to plan TKA without further weight bearing imaging in routine cases

Aims. Leg length discrepancy (LLD) is a common pre- and postoperative issue in total hip arthroplasty (THA) patients. The conventional technique for measuring LLD has historically been on a non-weightbearing anteroposterior pelvic radiograph; however, this does not capture many potential sources of LLD. The aim of this study was to determine if long-limb EOS radiology can provide a more reproducible and holistic measurement of LLD. Methods. In all, 93 patients who underwent a THA received a standardized preoperative EOS scan, anteroposterior (AP) radiograph, and clinical LLD assessment. Overall, 13 measurements were taken along both anatomical and functional axes and measured twice by an orthopaedic fellow and surgical planning engineer to calculate intraoperator reproducibility and correlations between measurements. Results. Strong correlations were observed for all EOS measurements (r. s. > 0.9). The strongest correlation with AP radiograph (inter-teardrop line) was observed for functional-ASIS-to-floor (functional) (r. s. = 0.57), much weaker than the correlations between EOS measurements. ASIS-to-ankle measurements exhibited a high correlation to other linear measurements and the highest ICC (r. s. = 0.97). Using anterior superior iliac spine (ASIS)-to-ankle, 33% of patients had an absolute LLD of greater than 10 mm, which was statistically different from the inter-teardrop LLD measurement (p < 0.005). Discussion. We found that the conventional measurement of LLD on AP pelvic radiograph does not correlate well with long leg measurements and may not provide a true appreciation of LLD. ASIS-to-ankle demonstrated improved detection of potential LLD than other EOS and radiograph measurements. Full length, functional imaging methods may become the new gold standard to measure LLD. Cite this article: Bone Jt Open 2022;3(12):960–968

Background. The advent of EOS imaging has offered clinicians the opportunity to image the whole skeleton in the anatomical standing position with a smaller radiation dose than standard spine roentgenograms. It is known as the fifth modality of imaging. Current NICE guidelines do not recommend EOS scans over x-rays citing: “The evidence indicated insufficient patient benefit in terms of radiation dose reduction and increased throughput to justify its cost”. Methods. We retrospectively reviewed 103 adult and 103 paediatric EOS scans of standing whole spines including shoulders and pelvis for those undergoing investigation for spinal deformity in a tertiary spinal centre in the UK. We matched this against a retrospective control group of 103 adults and 103 children who underwent traditional roentgenograms whole spine imaging at the same centre during the same timeframe. We aimed to compare the average radiation dose of AP and lateral images between the two modalities. We utilised a validated lifetime risk of cancer calculator (. www.xrayrisk.com. ) to estimate the additional mean risk per study. Results. In the Adult EOS Group (AEG) the mean estimated effective dose of AP was 0.08 mSv (0.04–0.15) and Lateral 0.06 mSv (0.03–0.14). Conversely in the Adult Roentgenograms Group (ARG) the mean AP was 0.49 mSv (0.15–1.88) and Lateral was 0.29 mSv (0.07–1.20). In the Paediatric EOS Group (PEG): the mean dose of AP was 0.07 mSv (0.02–0.21) and Lateral 0.04 mSv (0.02–0.11). Conversely Paediatric Roentgenograms Group (PRG) had a mean dose in AP of 0.37 mSv (0.03–5.92) and in lateral of 0.17 mSv (0.03–0.44). The percentage differences were: ARG:AES AP 613%, ARG:AES Lat 483%, PPG:PEG AP 529%, PRG:PEG Lat 425%. Mean difference 513%. The additional lifetime cancer risk for AEG was 1 in 176056 for males and 1 in 138696 for females, compared to ARG 1 in 31596 for males and 1 in 24894 for females. In PEG that was 1 in 58207 for boys and 1 in 33367 for girls, compared to PRG 1 in 11860 for boys and 1 in 6797 in girls. Differences in additional lifetime risk of cancer per scan: ARG:AES Male 557%, Female 557%, PRG:PEG Male 491%, Females 491%. Conclusion. Standard plain film imaging of the whole spine requires approximately five-times higher doses of radiation compared to dual planar EOS scans. This carries a significant impact when considering the need for repeat imaging on additional lifetime malignancy risk in both children and adults. There is approximately 5-fold increase in risk of cancer for all groups with roentgenograms over EOS. We directly challenge the NICE guidance and recommend EOS dual planar imaging in favour of plane roentgenograms for investigation of spinal deformity

Background. Digital templating is a critical part of preoperative planning for total hip arthroplasty (THA) that is increasingly used by orthopaedic surgeons as part of their preoperative planning process. Digital templating has been used as a method of reducing hospital costs by eliminating the need for acetate films and providing an accurate method of preoperative planning. Pre-operative templating can help anticipate and predict appropriate component sizes to help avoid postoperative leg length discrepancy, failure to restore offset, femoral fracture, and instability. A preoperative plan using digital radiographs for surgical templating for component size can improve intraoperative accuracy and precision. While templating on conventional and digital radiographs is reliable and accurate, the accuracy of templating on digital images acquired with a novel biplanar imaging system (EOS Imaging Inc, Cambridge, MA, USA) remains unknown. EOS imaging captures whole body images of a standing patient without stitching or vertical distortion, less magnification error and exposes patients to less radiation than a pelvis AP radiograph. Therefore, the purpose of this study was to compare EOS imaging and conventional anteroposterior (AP) xrays for preoperative digital templating for THA, and compare the results to the implant sizes used intraoperatively. Methods. Forty primary unilateral THA patients had preoperative supine AP xrays and standing EOS imaging. The mean age for patients was 61 ± 8 years, the mean body mass index 29 ± 6 kg/m. 2. and 21 patients were female. All patients underwent a THA with the same THA system (R3 Acetabular System and Synergy Cementless Stem, Smith & Nephew, TN, USA) by a single surgeon. Two blinded observers preoperatively templated using both AP xray and EOS imaging for each patient to predict acetabular size, femoral component size, and stem offset. All templating was performed by two observers with standard software (Ortho Toolbox, Sectra AB, Linköping, Sweden) [Figure 1] one week prior to surgery, and were compared using the Cronbach's alpha (∝) coefficient of reliability. The accuracy of templating was reported as the average percent agreement between the implanted size and the templated size for each component. Results. For templating acetabular component size, the exact size was predicted for 48% using AP xrays and 70% using EOS imaging, and within 1 size for 88% using xrays and 98% using EOS imaging. For templating femoral component size, the exact size was predicted exactly for 33% using AP xrays and 60% using EOS imaging, and within 1 size for 85% using xrays and 98% using EOS imaging (Figure 2). Interobserver agreement was excellent for acetabular components (Cronbach's α = 0.94) and femoral components (Cronbach's α = 0.96) using EOS imaging. Conclusions. This study demonstrates that preoperative digital templating for THA using EOS imaging is accurate, with excellent interobserver agreement. EOS imaging has less magnification error, which may partially explain the accuracy of our templating method

Background. Achieving optimal prosthesis alignment during total knee arthroplasty (TKA) is essential. Imageless computer-assisted surgery (CAS) is developed to improve knee prosthesis alignment and with CAS it is possible to perform intraoperative alignment measurements. Lower limb alignment measurements are also performed for preoperative planning and postoperative evaluation. A new stereoradiography system, called EOS, can be used to perform these measurements in 3D and thus measurement errors due to malpositioning can be eliminated. Since both CAS and EOS are based on 3D modeling, measurements should theoretically correlate well. Therefore, objective was to compare intraoperative CAS-TKA measurements with pre- and postoperative EOS 3D measurements. Methods. In a prospective study 56 CAS-TKAs were performed and alignment measurements were recorded two times: before bone cuts were made and after implantation of the prosthesis. Pre- and postoperative coronal alignment measurements were performed using EOS 3D. CAS measurements were compared with EOS 3D reconstructions. Measured angles were: varus/valgus (VV), mechanical lateral distal-femoral (mLDFA) and medial proximal tibial angle (mMPTA). Results. Significantly different VV angles were measured pre- and postoperatively with CAS compared to EOS. For preoperative measurements, mLDFA did not differ significantly, but a significantly larger mMPTA in valgus was measured with CAS. Conclusions. EOS 3D measurements overestimate VV angle in lower limbs with substantial mechanical axis deviation. For lower limbs with minor mechanical axis deviation as well as for mMPTA measurements, CAS measures more valgus compared to EOS. Results of this study indicate that differences in alignment measurements between CAS measurements and pre- and postoperative EOS 3D are mainly due to the difference between weight bearing and non-weight bearing position and potential errors in validity and reliability of the CAS system. Surgeons should be aware of these measurement differences and the pitfalls of both measurement techniques. Level of evidence. IIb. Disclosures. The department of Orthopaedics, University of Groningen, University Medical Center Groningen receives research institutional support from InSpine (Schiedam, NL) and Stryker (Kalamazoo, Mich. USA). One of the authors (ALB) will be and has been paid as a consultant by Zimmer (Warsaw, IN, USA) for purposes of education and training in knee arthroplasty

Purpose of the study: Leg length discrepancy after THA is a common complication and source of recurrent complaints from patients. To date, no reliable and reproducible technique has come forward to enable accurate quantification of all radiological parameters of the lower limb. Nevertheless, preoperative planning for hip arthroplasty requires knowledge of many limb parameters, in particularly leg length discrepancy, femoral offset, or the head-neck angle. The most widely used method is to use the 2D radiographs. The EOS system uses two digitalised 2D images taken orthogonally in a weight-bearing position to enable 3D reconstruction of the lower limb. The inter- and intraoperator reproducibility has been studied and validated. The purpose of our study was to compare the inter- and intra-operator reproducibilities of the measures taken on the standard full-length x-ray and those determined on the 3D EOS reconstructions. Material and method: Twenty-five patients scheduled for THA were included in this study (50 lower limbs). Two independent operators determine the measures on the AP EOS view and on the 3D reconstructions obtained from two orthogonal EOS images. The following parameters were measured: femur length, tibia length, limb length, HKA, HKS, femoral offset, neck-shaft angle, head diameter, and length of the femoral neck. Each observer performed two series of measurements. Interobserver reproducibility was assessed with the intraclass correlation coefficient (CI: 95%). Student’s t test was used to compare the clinical parameters measured on the 2D and 3D images. Results: Inter- and intraobserver reproducibility were 0.867 and 0.903 on the 2D x-rays and 0.911 and 0.940 on the 3D reconstructions. The better reproducibility of the EOS reconstruction was confirmed for all parameters tested in this study. Comparison of the 3D and 2D measurements revealed significant differences. Discussion: Our study demonstrated that measurements made on EOS 3D reconstructions offer better inter- and intraobserver reproducibility than those made on the standard AP view. In addition, the 3D reconstruction takes into consideration of the projection of the anatomic structures in the plane of the AP radiograph. The EOS appears to be a pertinent tool giving reliable results for the pre- and postoperative work-up for arthroplasty of the lower limb

Introduction. The safe zone of the acetabular cup for THA was discussed based on the AP X-ray films of hip joints. A supine position is still used to determine the cup position for CAOS such as navigation systems. There were few data about the implant positions after THA in standing positions. The EOS X-Ray Imaging Acquisition System (EOS system) (EOS imaging Inc, Paris, France) allows image acquisition with the patients in a standing or sitting position. We can obtain AP and lateral X-ray images with high-quality resolution and low dose radiation exposure. Recently, we have obtained the EOS system for the first time in Japan. We investigated 3D accuracy of the EOS system for implant measurements after THA. Patients and Methods. We measured the implant angles of the 68 patients (59 females and 9 males, average age: 61y.o.) who underwent THA using the EOS system. The cup inclination and anteversion were measured in the anterior pelvic plane (APP) coordinate. The femoral stem antetorsion was defined as angles between the stem neck axis and the posterior condylar axis. These data were compared with the implant angles of the same patients measured by the post-operative CT scan images and the 3D image analysis using the ZedHip software (LEXI, Japan). Results. The cup inclinations (average ±SE) measured by the EOS system and the CT scan were 40.6 ± 0.64° and 42.9 ± 0.53°, respectively. The cup anteversions were 22.9 ± 1.3° and 22.8 ± 1.0°, respectively. The stem antetorsions were 28.9 ± 1.3° and 29.8 ± 1.6°, respectively. The differences (average ± SE) between the EOS system and the CT scan in the cup inclination, the cup anteversion, and the stem antetorsion were −2.3 ± 0.38°, −0.09 ± 0.82°, and −0.90 ± 0.91°, respectively. There were strong correlations in measurement values between the EOS system and the CT scan (the Spearman's correlation coefficients of the cup inclination, the cup anteversion, and the stem antetorsion were 0.6521 [p<0.001], 0.7154 [p<0.001], and 0.8645 [p<0.001], respectively). Discussion. The EOS system provides acceptable clinical accuracies in measuring acetabular cup and femoral stem angles after THA. The accuracy of the cup angles was accorded with that of the basic experimental data using a dry pelvis. Our data also demonstrated clinically acceptable accuracy in the measurement of stem antetorsion. This system can provide accurate snap shots of variable postures with high resolution. Using the EOS system, we may establish real optimum positions of THA implants by measuring the patients after THA in several postures including standing, squatting or sitting positions which required for Japanese ADL

Unlike conventional radiographic methods, the newly introduced EOS system provides simultaneously-synchronized anteroposterior (AP) and true-lateral (LAT) x-ray images. EOS offers considerable potential for calculating parameters such as true femoral and acetabular angular positioning, impingement sites, and also for measuring wear in polyethylene cups. In this study we used THA wear-simulation fixtures to assess 3D-wear in polyethylene cups using EOS algorithms. Material and methods. A validated phantom apparatus was used to simulate values of three-dimensional wear, controlled in the 3 directions (antero-posterior, medio-lateral, cranio-caudal) using micrometers. (Figure 1). 24 simulations of wear with controlled amplitudes and directions were imaged using the biplane EOS slot-scanning system. Wear amplitudes were between 0 and 3464 μm. Using dedicated software, wear was measured by a 2D/3D matching of 3D spheres onto the 2D frontal and lateral radiographs, allowing the determination of the 3D coordinates of both the cup and femoral head centers and thus the calculation of a 3D wear vector. (Figure 2). Measured wear vector were compared to real wear vectors in terms of amplitude and direction.3D wear vectors were measured twice by 3 independent observers (for a total of 144 measurements) in order to evaluate intra- and inter-observer reliability. Results. There was a strong correlation between the measured wear amplitude and the real wear amplitude (Pearson's r = 0,99). Mean error when comparing wear measurement amplitude with real wear amplitude was 356 μm (SD = 127 μm). None of the 144 measurements presented an error over 1 mm. The accuracy of wear direction evaluation was highly correlated with wear amplitude (Spearman's rho = 0,98), the measurement of 3D wear direction presenting an accuracy better than 15° for wear amplitudes over 1,5 mm. Intra-observer errors for wear amplitude were between 138 μm and 221 μm depending on the observer. Inter-observer error for wear amplitude was 333 μm. Conclusion. EOS imaging is a promising technology for measuring 3D-wear in polyethylene cups. Further works are underway to compare the EOS algorithms with conventional methods

Introduction. Studies show that cup malpositioning using conventional techniques occurs in 50 to 74% of cases defined. Assessment of the utility of improved methods of placing acetabular components depends upon the accuracy of the method of measuring component positioning postoperatively. The current study reports on our preliminary experience assessing the accuracy of EOS images and application specific software to assess cup orientation as compared to CT. Methods. Eighteen patients with eighteen unilateral THA had pre-operative EOS images were obtained for preoperative assessment of leg-length difference and standing pelvic tilt. All of these patients also had preoperative CT imaging for surgical navigation of cup placement. This allows us to compare cup orientation as measured by CT to cup orientation as measured using the EOS images. Application specific software modules were developed to measure cup orientation using both CT and EOS images (HipSextant Research Application 1.0.13 Surgical Planning Associates Inc., Boston, Massachusetts). Using CT, cup orientation was determined by identifying Anterior Pelvic Plane coordinate system landmarks on a 3D surface model. A multiplanar reconstruction module allows for creation of a plane parallel with the opening plane of the acetabulum and subsequent calculation of plane orientation in the AP Plane coordinate space according to Murray's definitions of operative anteversion and operative inclination. Using EOS DICOM images, spatial information from the images were used to reconstruct the fan beam projection model. Each image pair is positioned inside this projection model. Anterior Pelvic Plane coordinate points are digitized on each image and back-projected to the fan beam source. Corresponding beams are then used to compute the 3D intersection points defining the 3D position and orientation of the Anterior Pelvic Plane. Ellipses with adjustable radii were then used to define the cup border in each EOS image. By respecting the fan beam projection model, 3D planes defining the projected normal of the ellipse in each image are computed. 3D implant normal was estimated by determining 3D plane intersection lines for each image pair. Implant center points are defined by using the back-projected and intersected ellipse center beams in the image pairs (Figure 1). Results. The results are shown in Figure 2. The mean anteversion error was −0.9 degrees (SD 4.1, range −6.9 to 10.3). The mean inclination error was 1.8 (SD 2.1, range −2.9 to 8.6). All three cups with errors greater than 7 degrees were in cups with 40 or more degrees of anteversion. Discussion and Conclusion. The current study, while very preliminary, demonstrates the potential that EOS images can be used to measure cup orientation with a reasonable degree of accuracy. Accurate determination of cup orientation appears to be more challenging in cups with higher anteversion

Purpose of the study: The analysis of hip prostheses often remains limited to standard x-rays taken in the upright position or a CT scan taken in the supine position. The EOS. ®. system enables imaging the entire body for head to foot in a lateral and anteroposterior views, in an upright or sitting position. The purpose of this work was to compare the standard radiographic work-up with the EOS system for the analysis of postural elements in patients with hip arthroplasty. Material and method: This prospective study included 50 patients free of complications. The standard radiographic work-up included AP and lateral views in the upright and sitting positions. The standard then EOS imaging protocols were performed in two different locations. Images were acquired with the patients in a comfortable position: for the sitting position, the knees were flexed 90°. Two operators took measurements to be able to analyse reproducibility of the morphological parameters (incidence, sacroacetabular angle, and the positional parameters (version, sacral slope, Lewinnek angle, sagittal and frontal cup inclinations, pelvifemoral angle and orientation of the prosthetic neck on the lateral standing then AP sitting position). Pelvic rotation was determined on the AP view by comparative measurement of the projected width of the iliac wings in each pelvis. Hip extension reserve was calculated on the hyperextension lateral view. Results: Reproducibility of position was excellent for different times and locations. Twelve hip (24%) presented significant reproducible rotation in the AP view; for eight of these hips (16%), the phenomenon disappeared in the sitting position. Four hips (8%) had pelvic rotation in the sitting position on the AP view. On the AP pelvic view in the sitting position, three patients had a femoral neck in functional retroversion while the anatomic femoral anteversion was normal on the scanner. The pelvic parameters were equivalent to those already described. The reproducibility of the measures was excellent between the standard x-rays and the EOS images with the exception of measurements involving the centre of the femoral head (incidence, pelvifemoral angle). It was easier to align the femoral axis on the EOS lateral images, particularly for additional calculation of extension reserve. The Lewinnek angle could not be measured in the sitting position in 32 hips (60%) because of insufficient resolution. Conclusion: The overall evaluation of the pelvis and the subpelvic sector provides new information concerning the respective positions of the cup and the femur in functional situations

The anterior pelvic plane (APP) angle is often used as a reference to decide pelvic alignment for hip surgeons. However, Rousseau criticised the validness of the APP angles because the APP angles in standing position measured on conventional standing X-ray films never showed correlation with the other pelvic alignment parameters, such as sacral slope (SS). We measured the APP angles, SS and pelvic tilt (PT) on the non-distorted anteroposterior (AP) and lateral digitally reconstructed radiography (DRR) images in supine position (with CT scans) and AP and lateral X-ray images in standing position (with EOS X-ray machine [EOS imaging, Paris, France]) by using of the same EOS software. Our data showed that the pre- and post-operative APP angles correlated with SS and PT in both supine and standing positions. Our non-distorted high quality images and the EOS software revealed these correlations. Therefore, we can still use the APP angles to decide pelvic alignment for patients who undergo total hip arthroplasty (THA). Recent papers demonstrated positional or chronological dramatic changes of the APP angles between pre- and post-operative states in patients who underwent THA. The EOS system will be a powerful tool to investigate these changes of the pelvic alignments

Introduction. Most of studies on Total Hip Arthroplasty (THA) are focused on acetabular cup orientation. Even though the literature suggests that femoral anteversion and combined anteversion have a clinical impact on THA stability, there are not many reports on these parameters. Combined anteversion can be considered morphologically as the addition of anatomical acetabular and femoral anteversions (Anatomical Combined Anatomical Anteversion ACA). It is also possible to evaluate the Combined Functional Anteversion (CFA) generated by the relative functional position of femoral and acetabular implants while standing. This preliminary study is focused on the comparison of the anatomical and functional data in asymptomatic THA patients. Material and methods. 50 asymptomatic unilateral THA patients (21 short stems and 29 standard stems) have been enrolled. All patients underwent an EOS low dose evaluation in standing position. SterEOS software was used for the 3D measurements of cup and femur orientation. Cup anatomical anteversion (CAA) was computed as the cup anteversion in axial plane perpendicular to the Anterior Pelvic Plane. Femoral anatomical anteversion (FAA) was computed as the angle between the femoral neck axis and the posterior femoral condyles in a plane perpendicular to femoral mechanical axis. Functional anteversions for the cup (CFA) and femur (FFA) were measured in the horizontal axial patient plane in standing position. Both anatomical and functional cumulative anteversions were calculated as a sum. All 3D measures were evaluated and compared for the repeatability and reproducibility. Statistical analysis used Mann-Whitney U-test considering the non-normal distribution of data and the short number of patients (<30 for each group). Results. Functional cumulative anteversion was significantly higher than anatomical cumulative anteversion for all groups (p<0.05). No significant difference could be noted between the cases according to the use of short or standard stems. Conclusion. This study shows the difference of functional implant orientation as compared to the anatomical measurements. This preliminary study has limitations. First the limited sample of patients. Then this series only includes asymptomatic subjects. Nevertheless, this work focused on the feasibility of the measurements shows the potential interest of a functional analysis of cumulated anteversion. Standing position influences the relative position of THA implants according to the frontal and sagittal orientation of the pelvis. The relevance of these functional measurements in instability cases must be demonstrated, especially in patients with anterior subluxation in standing position which is potentially associated with pelvic adaptative extension. Further studies are needed for the feasibility of measurements on EOS images in sitting position and their analysis in case of instability. For any figures or tables, please contact authors directly

Introduction. Optimal implant position is the important factor in the hip stability after THA. Both the acetabular and femoral implants are placed in anteversion. While most hip dislocations occur either in standing position or when the hip is flexed, preoperative hip anatomy and postoperative implants position are commonly measured in supine position with CT scan. The isolated and combined anteversions of femoral and acetabular components have been reported in the literature. The conclusions are questionable as the reference planes are not consistent: femoral anteversion is measured according to the distal femoral condyles plane (DFCP) and acetabulum orientation in the anterior pelvic plane (APP)). The EOS imaging system allows combined measurements for standing position in the “anatomical” reference plane or anterior pelvic plane (APP) or in the patient “functional” plane (PFP) defined as the horizontal plane passing through both femoral heads. The femoral anteversion can also be measured conventionally according to the DFCP. The objective of the study was to determine the preoperative and postoperative acetabular, femoral and combined hip anteversions, sacral slope, pelvic incidence and pelvic tilt in patients who undergo primary THA. Material and Methods. The preoperative and postoperative 3D EOS images were assessed in 62 patients (66 hips). None of these patients had spine or lower extremity surgery other than THA surgery in between the 2 EOS assessments. None had dislocation within the follow up time period. Results. Pelvic values. The preoperative sacral slope was 42.4°(11° to 76°) as compared to the postoperative sacral slope (40.3°, −4° to 64°)(p=0.014). The preoperative pelvic tilt was 15.3° (−10° to 44°) as compared to the postoperative tilt (17.2°, −6° to 47°)(p=0.008). The preoperative pelvic incidence was 57.7°(34° to 93°) and globally unchanged as compared to the postoperative incidence (57.5°, 33° to 79°)(p=0.8). Acetabular values. Surgeons increased the anteversion according to the APP by an average of 12.6°(−13° to 53°)(p<0.001). Acetabular anteversion was increased by 14.3° in the PFP (−11° to 51°)(p<0.001). Femoral values. In the DFCP, preoperative neck anteversion was decreased postoperatively by an average of −3,2°(−48° to 33°)(p=0,0942). In the PFP, preoperative neck anteversion was decreased postoperatively by an average of −6,3°(−47° to 17°)(p<0,001). Combined values. According to the classical methods (acetabular orientation in the APP and femoral anteversion in the DFCP), mean preoperative combined anteversion was 36.1° (4° to 86°) and was increased postoperatively to 45.5°(−12° to 98°)(p=0.0003). According to the PFP, mean preoperative combined anteversion was 30,7°(5° to 68°) and was increased postoperatively to 38,8°(−10° to 72°)(p=0,0001). Conclusion. This study reports two methods for the measurement of acetabular and femoral anteversion, “anatomical” according to the APP and DFCP and “functional” according to the PFP. Surgeons tend to increase the anteversion of the acetabular implant and to decrease femoral anteversion during the surgery. The trend is the same for postoperative evolution of values using the “anatomical” or the “functional” methods but numerical discrepancies are explained by significant APP orientation changes. The assessment of the true combined anteversion provides new perspectives to optimize our understanding of THA stability and function

Introduction. Post op cup anatomical and functional orientation is a key point in THP patients regarding instability and wear. Recently literature has been focused on the consequences of the transition from standing to sitting regarding anteversion, frontal and sagittal inclination. Pelvic incidence (PI) is now considered as a key parameter for the analysis of sagittal balance and sacral slope (SS) orientation. It's influence on THP biomechanics has been suggested. Interestingly, the potential impact of this morphological angle on cup implantation during surgery and the side effects on post op functional orientation have not been studied. Our study explores this topic from a series of standing and sitting post-op EOS images. Material and methods. 310 patients (mean age 63,8, mean BMI 30,2) have been included prospectively in our current post-operative EOS protocol. All patients were operated with the same implants and technique using anterior approach in lateral decubitus. According to previous literature, 3 groups were defined: low PI less than 45° (57 cases), high PI if more than 60° (63 cases), and standard PI in 190 other cases. Results. Mean PI was 55,8° (SD 11,5). -In High PI, postop SS in standing was significantly higher than in Low and Medium PI. In Medium PI, postop SS in standing was significantly higher than in Low PI. -In High PI, postop SS in sitting was significantly higher than in Low and Medium PI. -In Low PI, postop Functional anteversion in sitting was significantly higher than in Medium PI, but not different from High PI. -In Low PI, Anatomical anteversion was significantly higher than in Medium and High PI. Discussion, Conclusion. This preliminary study points out the potential influence of pelvis morphology expressed by PI on per-operative cup orientation. As surgeons are accustomed to follow bony landmarks during cup implantation, unexpected variations for cup adjustment may be observed if PI is not standard. For any figures or tables, please contact authors directly

Introduction. Coronal misalignment of the lower limbs is closely related to the onset and progression of osteoarthritis. In cases of severe genu varus or valgus, evaluating this alignment can assist in choosing specific surgical strategies. Furthermore, restoring satisfactory alignment after total knee replacement promotes longevity of the implant and better functional results. Knee coronal alignment is typically evaluated with the Hip-Knee-Ankle (HKA) angle. It is generally measured on standing AP long-leg radiographs (LLR). However, patient positioning influences the accuracy of this 2D measurement. A new 3D method to measure coronal lower limb alignment using low-dose EOS images has recently been developed and validated. The goal of this study was to evaluate the relevance of this technique when determining knee coronal alignment in a referral population, and more specifically to evaluate how the HKA angle measured with this 3D method differs from conventional 2D methods. Materials and methods. 70 patients (140 lower extremities) were studied for 2D and 3D lower limb alignment measurements. Each patient received AP monoplane and biplane acquisition of their entire lower extremities on the EOS system according the classical protocols for LLR. For each patient, the HKA angle was measured on this AP X-ray with a 2D viewer. The biplane acquisition was used to perform stereoradiographic 3D modeling. Valgus angulation was considered positive, varus angulation negative. Student's T-test was used to determine if there was a bias in the HKA angle measurement between these two methods and to assess the effect of flexion/hyperextension, femoral rotation and tibial rotation on the 2D measurements. One operator did measurements 2 times. Results. The average total dose for both acquisitions was 0.75mGy (± 0.11mGy). The 2D and 3D measurements are reported in table 1. Intraoperator reliability was >0,99 for all measurements. In the whole series, 2D–3D HKA differences were >2° in 34% of cases, >3° in 22% of cases, >5° in 9% of cases and >10° in 3% of cases >10°. We compared 2D and 3D measurements according to the degree of flessum/recurvatum (> or <5° and > or <10°). The results are reported in table 2. The statistical analysis of parameters influencing 2D/3D measurements is reported in table 3. Discussion and conclusion. The HKA angle is typically assessed from 2D long-leg radiographs. However, several studies highlighted that 2D assessment of this angle may be affected by patient's positioning. Radtke showed that lower limb rotation during imaging significantly affected measurements of coronal plane knee alignment. Brouwer showed that axial rotation had an even greater effect on the apparent limb alignment on AP radiographs when the knee was flexed. This last finding is particularly relevant as many lower extremities present some amount of flexion or hyperextension, especially in aging subjects. This low dose biplanar EOS acquisitions provide a more accurate evaluation of coronal alignment compared to 2D, eliminating bias due to wrong knee positioning. This study points out the interest of EOS in outliers patients and opens new perspectives for preoperative planning and postoperative control of deformity correction or knee joint replacement

Introduction: Degenerative osteoarticular conditions of the lower limb comprise of the most common orthopedic diseases requiring implants surgery. Biomechanical factors have an important role in the development of the degenerative process. Radiological diagnostics prominently rely on bidirectional 2D X-ray images, CT and MRI also being employed in the assessment process. However, these diagnostic tools usually cover a single joint, mostly unilaterally, rarely if ever providing a chance to simultaneously examine each members of the closed kinetic chain of both limbs under normal postural loads in a standing position. Classification and measurements of anatomical conditions are carried out in a 2D environment only and measured values are projected to real-life circumstances. EOS, a new 2D/3D digital imaging system based on Nobel-prize winning ultra low-dose X-ray radiation detection and a unique 3D toolbox with 3D reconstruction module offers a truly groundbreaking option in this field. We present results obtained during the first year of clinical use of our EOS 2D/3D system. Methods: 20 patients with coxarthrosis and 20 patients with gonarthrosis have been examined with traditional 2D X-ray and EOS 2D/3D system. Clinical parameters (femoral and tibial length, mechanical angle of the femur and tibia, anatomical and mechanical femorotibial angle, etc.) have been determined for both diagnostic methods and results were compared. 3D measurements available within EOS 3D toolbox were determined including femoral and tibial torsion and femorotibial rotation. For visualization of the lower limbs EOS 3D reconstructions were made. Results: Using EOS built-in 3D toolbox, comparison of numerical data for 2D and 3D measurements of clinical parameters showed a significant difference whereby 3D measurements always represented more valid, more accurate values. Differences between 2D and 3D measurement values were as much as 5–10 mm in length or 5–8 degrees in angles. This was particularly true for conditions where torsion and rotation of the bones were present. EOS 3D reconstruction module provided a surface reconstructed 3D model of the examined limbs and automatically displayed every clinically relevant parameters measured in the 3D toolbox. This proved to be an important feature for pre-operative planning and postoperative evaluations. Conclusion: EOS 2D/3D system provides a ground-breaking new tool for length and angle measurements of the lower limb in 3D, providing distortion-free clinical parameters that are accurate and true-to-life values, avoiding artefactual effects from projection, torsion and rotation and positioning of the patient, which usually concomitantly affect the accuracy and reproducibility of conventional 2D measurements

Introduction. The assessment of leg length is essential for planning the correction of deformities and for the compensation of length discrepancy, especially after hip or knee arthroplasty. CT scan measures the “anatomical” lengths but does not evaluate the “functional” length experienced by the patients in standing position. Functional length integrates frontal orientation, flexion or hyperextension. EOS system provides simultaneously AP and lateral measures in standing position and thus provides anatomical and functional evaluations of the lower limb lengths. The objective of this study was to measure 2D and 3D anatomical and functional lengths, to verify whether these measures are different and to evaluate the parameters significantly influencing these potential differences. Material and Methods. 70 patients without previous surgery of the lower limbs (140 lower extremities) were evaluated on EOS images obtained in bipodal standing position according to a previously described protocol. We used the following definitions:. anatomical femoral length between the center of the femoral head (A) and center of the trochlea (B). anatomical tibial length between the center tibial spine (intercondylar eminence) (C) and the center of the ankle joint (D). functional length is AD. global anatomical length is AB + CD. Other parameters measured are HKA, HKS, femoral and tibial mechanical angles (FMA, TMA), angles of flexion or hyperextension of the knee, femoral and tibial torsion, femoro-tibial torsion in the knee, and cumulative torsional index (CTI). All 2D et3D measures were evaluated and compared for their repeatability. Results. Regarding repeatability, an ICC> 0.95 was found for all measurements except for the tibial mechanical angle (0.91 for 2D, 3D 0.92 for 3D). We observed 54/140 lower limbs with Flessum/Recurvatum angles (FRA) >10°. 2D results (mean, SD) were. 41,8mm(2,9) for femoral anatomical length. 36,1mm(2,8) for tibial anatomical length. 78,0mm(5,4) for global anatomical length. 78,5 mm(5,5) for functional length. 7,4°(12,0) for Flessum/Recurvatum angle. −1,5°(6,4) for HKA. 4,9°(2,0) for HKS. 92,1°(3,4) for FMA. 87,1°(3,4) for TMA. 3D results (mean, SD) were. 42,4mm (2,8) for femoral anatomical length. 36,6mm (2,8) for tibial anatomical length. 79,0mm (5,4) for global anatomical length. 78,9mm (5,5) for functional length. 7,2°(12,0) for Flessum/Recurvatum angle. −1,0°(5,9) for HKA. 4,9°(1,5) for HKS. 92,7°(2,7) for FMA. 87,9°(3,9) for TMA. The 2D/3D measurements of functional lengths were statistically significant (p <0.0001. Student's test). For anatomical lengths. 2D/3D measurements were also statistically significant (p <0.0001. Student's test for femoral tibial and global anatomical lengths). Some parameters significantly influenced 2D/3D differences:. for the global anatomical length: FRA P<0,0001, TMA P=0,0173, HKA P=0,0259 and femoro-tibial torsion P=0,0026. for the functional length FRA P=0,0065. Discussion and conclusion. EOS imaging allows to accurately assess the anatomical and functional length experienced by the patient. These new data open new perspectives for planning length or axis corrections and for an optimized evaluation in some medico legal issues after joint replacement or posttraumatic sequelae. This study points out the importance of 3D measurements in outliers cases (varus or valgus cases, flessum or recurvatum of the knee)

Introduction. Pelvic flexion and extension in different body positions can affect acetabular orientation after total hip arthroplasty, and this may predispose patients to dislocation. The purpose of this study was to evaluate functional acetabular component position in total hip replacement patients during standing and sitting. We hypothesize that patients with degenerative lumbar disease will have less pelvic extension from standing to sitting, compared to patients with a normal lumbar spine or single level spine disease. Methods. A prospective cohort of 20 patients with primary unilateral THR underwent spine-to-ankle standing and sitting lateral radiographs that included the lumbar spine and pelvis using EOS imaging. Patients were an average age of 58 ± 12 years and 6 patients were female. Patients had (1) normal lumbar spines or single level degeneration, (2) multilevel degenerative disc disease or (3) scoliosis. We measured acetabular anteversion (cup relative to the horizontal), sacral slope angle (superior endplate of S1 relative to the horizontal), and lumbar lordosis angles (superior endplates of L1 and S1). We calculated the absolute difference in acetabular anteversion and the absolute difference in lumbar lordosis during standing and sitting (Figure 1). Results. Nine patients had normal lumbar spines or scoliosis, and 11 patients had multilevel disc disease. The median change in cup anteversion for normal and scoliosis patients was 29° degrees (range 11° to 41°) compared to 21° degrees (range 1° to 34°) for multilevel disc disease patients (p=0.03). There was a positive correlation between the change in cup anteversion and the change in lumbar lordosis (p=0.01; Figure 2). From standing to sitting, cup anteversion always increased and lumbar lordosis always decreased. Conclusions. The change in cup anteversion from standing to sitting was variable in patients with normal, degenerative, and scoliosis lumbar spines. Patients with degenerative disc disease have less pelvic extension, and thus less acetabular anteversion in the sitting position compared to normal spines. This may increase their risk of posterior dislocation

Introduction. The gold standard for knee surgery is the restoration of the so-called «neutral mechanical alignment ». Recent literature as pointed out the patients with «constitutional varus »; in these cases, restoring neutral alignment could be abnormal and even undesirable. The same situation can be observed in patients with «constitutional valgus alignment ». To date, these outliers cases have only been explored focusing on the lower limb; the influence of the pelvic morphotype has not been studied. Intuitively, the pelvic width could be a significant factor. The EOS low dose imaging technique provides full body standing X-rays to evaluate the global anatomy of the patient. This work explores the influence of the pelvic parameters on the frontal knee alignment. Material and methods. – We included 170 patients (340 lower extremities). 2 operators performed measurements once per patient on AP X-rays. The classical anatomical parameters were:. –. Femoral mechanical angle (FMA). –. Tibial mechanical angle (TMA). –. Hip knee shaft angle (HKS). –. Hip knee ankle angle (HKA). –. Femoral and tibial lengths. The morphotype was evaluated by:. –. the distances between the center of two femoral heads (FHD), between knees (KD) and between ankles (AD). –. the medial neck-shaft angle (MNSA). –. the femoral offset. The horizontal distance between the limb mechanical axis (line passing from center of the femoral head to the center of the ankle) and the center of the knee was called the intrinsic mechanical axis deviation (IMAD) (fig 1). The horizontal distance between the pelvic mechanical axis (line from the center of the sacral plate to the center of the ankle) and the center of the knee was called the global mechanical axis deviation (GMAD) (fig 2). Inter-Operator Reliability was calculated with Intra-class Correlation Coefficient (ICC) and Inter-Reader Agreement was assessed with Bland-Altman test. A relationship between IMAD and GMAD to the other parameters was assessed using Pearson's correlation coefficient. Results. Inter-Operator Reliability was high for femoral offset, TMA and MSNA (ICC > 0,88) and very high for the other parameters (ICC > 0,93). These values are given in table 1 and all the 2D parameters are given in the table 2. IMAD was significantly correlated with HKA (r = 0,99), FMA (r = −0,58), TMA (r = −0,61) and KD (r = 0,72). GMAD was significantly correlated with HKA (r = 0,94), FMA (r = −0,53), TMA (r = −0,60) and KD (r = 0,67). Two groups were identified according to pelvic width (FHD):. Group 1 (standard patients): Pelvic width < 18 cm (164 lower extremities). Group 2 (wide pelvis): Pelvic width ≥ 18 cm (176 lower extremities). For standard patients the FHD is a significant parameter, whereas the proximal femoral anatomy (offset and MNSA) are more relevant for wide pelvis. Conclusion. Accurate analysis of the morphotype of the lower limbs is essential for planning femoral or tibial osteotomy and knee prostheses. Taking into account pelvic morphotype can provide additional informations for the axes restoration and the detection of outliers patients